Low modulus belt for automotive applications

ABSTRACT

The invention provides a low modulus drive belt for an automotive accessory drive system that allows for relatively high elongation during installation and that maintains a relatively high percentage of its install tension throughout the useful life of the belt. The invention also provides an automotive accessory drive system that utilizes such a belt and a method for constructing such a belt. One embodiment of the invention is directed to an accessory drive system for an automobile that includes: (a) a drive pulley; (b) an accessory pulley operatively coupled to an accessory drive shaft; and (c) an endless drive belt engaged between the drive pulley and the accessory pulley, where the drive belt includes an endless band of rubber composite material having a plurality of circumferentially extending an axially aligned polyamide 6.6 twisted cords formed therewithin.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. application Ser. No.09/848,132 filed May 3, 2001.

BACKGROUND

[0002] The present invention is directed to a multiple-pulley accessorydrive system for an automobile; and more specifically, to an accessorydrive belt for such an accessory drive system.

[0003] The present invention was specifically developed to address theneed for an accessory drive belt capable of relatively easy installationby stretching the drive belt over the pulleys of the multiple-pulleyaccessory drive system, where this drive belt maintains sufficienttension throughout the design life of the drive system.

SUMMARY

[0004] The present invention provides a low modulus drive belt for anautomotive, multiple-pulley accessory drive system that allows forrelatively high elongation during installation and that maintains arelatively high percentage of its install tension throughout the usefullife of the belt. The present invention also provides an automotive,multiple-pulley accessory drive system that utilizes such a belt andprovides a method for constructing such a belt.

[0005] A first aspect of the present invention is directed to amultiple-pulley accessory drive system for an automobile that comprises:(a) a drive pulley; (b) an accessory pulley operatively coupled to anaccessory drive shaft; and (c) an endless drive belt engaged between thedrive pulley and the accessory pulley, where the drive belt includes anendless band of rubber composite material having a plurality ofcircumferentially extending an axially aligned polyamide 6.6 twistedcords formed therewithin and the belt's tensile modulus per width isabout 400 to 1500 N/mm. Tensile modulus per width is expressed as force(N) per % elongation (mm/mm) per 1 mm belt width, i.e., N/mm. In a moreparticular embodiment, the tensile modulus per width of the belt isabout 400 to 1200 N/mm. In a still more particular embodiment, thetensile modulus per width of the belt is about 600 to 1000 N/mm.

[0006] Tensile modulus per width is determined by plotting tension (T)versus elongation for the belt and determining the slope of the best-fitline where elongation is the change in belt length when tensioned by aforce T divided by the belt length when tensioned by the initialpre-load tension. The slope (m) divided by the belt width (mm) is thetensile modulus per width.

[0007] In a more detailed embodiment of this first aspect of theinvention, the circumferential length of the endless drive belt, beforeinstallation of the pulleys, is approximately 2% to approximately 3%lower than the nominal drive length of the accessory drive system. In afurther detailed embodiment, the circumferential length of the endlessdrive belt, before installation on the pulleys, is approximately 2% toapproximately 2.3% lower than the nominal drive length of the accessorydrive system. In yet a further detailed embodiment, the axial distancebetween the distant cords is approximately 0.80 mm to approximately 1.0mm. In yet a further detailed embodiment, each twisted cord includes apair of yarn strands twisted together. In yet a further detailedembodiment, each cord has diameter of approximately 0.58 mm (0.023 in.).

[0008] In an alternative detailed embodiment of the first aspect of thepresent invention, the endless drive belt has a tensile modulus ofapproximately 7000 N/mm/mm (1575 lbf/in/in) to approximately 10,000N/mm/mm (2250 lbf/in/in); and in an even more detailed embodiment, theendless drive belt has a tensile modulus of approximately 7800 N/mm/mm(1750 lbf/in/in) to approximately 8,500 N/mm/mm (1910 lbf/in/in). In yeta further detailed embodiment, the circumferential length of the endlessdrive belt, before installation on the pulleys, is approximately 2% toapproximately 3% lower than the nominal drive length of the accessorydrive system.

[0009] In another alternative embodiment to the first aspect of thepresent invention, the operational torque of the accessory drive systemis less than, or equal to approximately 2.7 N-m (2 ft-lb). In a furtherdetailed embodiment, the accessory is an automotive water pump, and theaccessory pulley is operatively coupled to a drive shaft of the waterpump.

[0010] It is a second aspect of the present invention to provide amultiple-pulley accessory drive system for an automobile that includes:(a) a drive pulley; (b) an accessory pulley operatively coupled to anaccessory drive shaft; (c) an endless drive belt engaged between thedrive pulley and the accessory pulley, where the drive belt includes anendless band of rubber composite material having a plurality ofcircumferentially extending and axially aligned cords formedtherewithin; (d) where the endless drive belt has a tensile modulus ofapproximately 7,000 N/mm/mm (1575 lbf/in/in) to approximately 10,000N/mm/mm (2250 lbf/in/in). In a further detailed embodiment, thecircumferential length of the endless drive belt, before installation onthe pulleys, is approximately 2% to approximately 3% lower than thenominal drive length of the accessory drive system. In yet a furtherdetailed embodiment, the circumferential length of the endless drivebelt, before installation on the pulleys, is approximately 2% toapproximately 2.3% than the lower nominal drive length of the accessorydrive system. In yet a further detailed embodiment, the cords arepolyamide twisted cords.

[0011] In an alternate detailed embodiment of the second aspect of thepresent invention the operational torque of the accessory drive systemis less than or equal to approximately 2.7 N-m (2 ft-lb). In a furtherdetailed embodiment, the accessory is an automotive water pump and theaccessory pulley is operatively coupled to a shaft of the water pump. Ina further detailed embodiment, the multiple-pulley accessory drivesystem is a two-pulley accessory drive system.

[0012] In an alternative detailed embodiment of the second aspect of thepresent invention, the endless drive belt has a tensile modulus ofapproximately 7,800 N/mm/mm (1750 lbf/in/in) to approximately 8,500N/mm/mm (1910 lbf/in/in).

[0013] It is a third aspect of the present invention to provide atwo-pulley accessory drive system for an automobile that includes: (a) adrive pulley; (b) an accessory pulley operatively coupled to accessorydrive shaft; (c) an endless drive belt engaged between the drive pulleyand the accessory pulley, where the drive belt includes an endless bandof rubber composite material having a plurality of circumferentiallyextending and axially aligned cords formed therewithin; (d) where theendless drive belt has a tensile modulus of approximately 8500 N/mm/mm(1910 lbf/in/in); and (e) where the circumferential length of theendless drive belt, before installation on the pulleys, is approximately2.2% to approximately 2.3% lower than the nominal drive length betweenthe drive pulley and the accessory pulley. In a further detailedembodiment the cords are polyamide 6.6 twisted cords.

[0014] A fourth aspect of the present invention is directed to amultiple-pulley system for an automobile that includes: (a) drivepulley; (b) an accessory pulley operatively coupled to an accessorydrive shaft; and (c) a endless drive belt engaged between the drivepulley and the accessory pulley, where the drive belt includes anendless band of rubber composite material having a plurality ofcircumferentially extending and axially aligned, polyamide 6.6 twistedcords formed therewithin; (d) where the circumferential length of theendless drive belt, before installation on the pulleys is approximately2.2% to approximately 2.3% lower than the nominal drive length of theaccessory drive system. In a further detailed embodiment, the axialdistance between the twisted cords is approximately 0.3 mm (0.012 in.)and each of the twisted cords includes a pair of cord yarns twistedtogether, where each cord has a diameter of approximately 0.58 mm (0.023in.).

[0015] In an alternate detailed embodiment of the fourth aspect of thepresent invention, the operational torque of the accessory drive systemis less than, or equal to approximately 2.7 N-m (2 ft-lbs). In a furtherdetailed embodiment, the accessory is an automotive water pump and theaccessory pulley is operatively coupled to a drive shaft of the waterpump.

[0016] A fifth aspect of the present invention is directed to a methodfor fabricating an accessory drive belt that includes the steps of: (a)applying at least a layer of fabric or rubber material to an outercircumferential surface of a drum; (b) applying at least a first layerof cushion stock rubber material to the drum over the fabric layer; (c)winding a polyamide 6.6 twisted cord to the drum over the first layer ofcushion stock; (d) applying a layer of relatively strong and wearresistant, fiber loaded, rubber material to the drum over the cords; (e)curing the multiple layers together into a cured sleeve of beltcomposite material; (f) cutting the cured sleeve into a plurality ofendless belts; and (g) turning the endless belt inside-out for use as anaccessory drive belt; (h) where the polyamide 6.6 twisted cord is woundin the winding step at approximately 3 lbf. (13 N) to approximately 3.5lbf. (15.5 N). In a more detailed embodiment, the winding step axiallyspaces the winds of the polyamide 6.6 twisted cord at approximately 0.40mm (26 cpi) to approximately 0.30 mm (30 cpi). In yet a further detailedembodiment the method further includes the step of, prior to the step ofturning the endless belt inside out, forming a plurality ofcircumferential grooves into the outer circumferential surface of thecured sleeve or of the endless belts. In an alternate detailedembodiment to the fifth aspect of the present invention, the methodincludes, after the winding step (c) and before the applying step (d),the step of (c1) applying at least a second layer of the cushion stockover the cords.

[0017] A sixth aspect of the present invention is directed to anaccessory drive belt for an automobile comprising a composite rubber andreinforcing cord composite, where the belt is adapted to be manuallystretched on the pulleys of the accessory drive system and has aninstall tension; and where the belt maintains approximately at least 40%of its install tension throughout the useful life of the belt. In adetailed embodiment, the belt maintains at least approximately 40% toapproximately 60% of its install tension throughout the useful life ofthe belt. In a further detailed embodiment, the cords in the compositeare polyamide 6.6 twisted cords.

[0018] The lower modulus belts used in accordance with this inventionhave advantages over higher modulus belts. In particular, the belts canbe designed for and used in applications in which lower installationtensions are desired or required. Because lower installation tensionsare available, the expected service life and, more particularly, thebearing life of the accessory driven by the belt will typically belonger. With a lower modulus belt the reduction/loss in modulus over thelife of the belt is less. This reduces installation tensionrequirements. Belts are conventionally installed at higher tension tocompensate for the loss in tension over the life of the belt. Becausethere will be less tension loss with a lower modulus belt, lowerinstallation tensions can be used. The belts can also be installed byhand in some applications.

DETAILED DESCRIPTION

[0019] The present invention provides a low modulus drive belt for anautomotive, multiplepulley accessory drive system that allows forrelatively high elongation during installation and that maintains arelatively high percentage of its install tension throughout the usefullife of the belt. The present invention also provides an automotive,multiple-pulley accessory drive system that utilizes such a belt andprovides a method for constructing such a belt.

[0020] As shown in FIG. 1, an example of a rear-end accessory drivesystem 10 for use in an automobile includes a drive pulley 12 driven bythe automobile's engine and an accessory pulley 14 operatively coupledto the drive shaft of the accessory component, such as the water pump ofthe automobile. A drive belt 16 is engaged between the pulleys 12, 14 totransfer rotational force from the drive pulley 12 to the accessorypulley 14. In an exemplary embodiment, the relative maximum speed forthis accessory drive system is approximately 3400 rpm with a relativemaximum torque of approximately 2.7 N-m (2 ft-lbs). Accordingly, in thisexemplary embodiment, the belt 16 for use with this drive maintains adrive tension of at least approximately 89 N (20 lbf.) and has aninstall tension of at most approximately 445 N (100 lbf). It will beappreciated that, while the accessory drive system of the exemplaryembodiment includes only two pulleys, it is within the scope of theinvention that the accessory drive system include more than two pulleys.

[0021] As shown in FIG. 2, the exemplary embodiment of the belt 16 is amulti-layer composite structure that includes an outer, cover layer 18of friction fabric material or rubber material bonded to a layer 20 ofcushion rubber material, which is bonded to an inner layer 22 ofwear-resistant rubber material. The layer 20 of cushion rubber material,in the exemplary embodiment, includes a plurality of axially aligned,polyamide 6.6 twisted cords 23 extending longitudinally therethrough.The inner layer 22 of wear-resistant rubber material is, in theexemplary embodiment, an EPDM compound selected according toenvironmental and performance factors that is impregnated withreinforcing fibers. Such a fiber-impregnated compound is shown, forexample, in U.S. Pat. Nos. 5,267,908 and 5,518,460 (see also, U.S. Pat.Nos. 5,273,496, 5,334,107, 5,507,699). Additionally, in the exemplaryembodiment, the cushion material in the layer 20 is an elastomericcompound compatible for curing with, and around the cords 23 andcompatible for bonding to the inner layer 22 of wear-resistant rubbermaterial. Additionally, in the exemplary embodiment, the polyamide 6.6twisted cords 23 are comprised of a pair of 6.6 polyamide yarn strandstwisted together, where the finished cord has a diameter ofapproximately 0.58 mm (0.023 in.). Such a construction is commonlyreferred to by those of ordinary skill in the art as a “840/1/2” cordconstruction (denier/yarns-per-ply/plies-per-cord). It will beappreciated to those of ordinary skill in the art that alternatearrangements of the 6.6 polyamide yarn strands can be used to createalternate constructions of the twisted cords that include, but are notlimited to, 840/1/2, 840/1/3, 1000/1/2, 660/1/3, etc. It has been foundthat a particularly desirable belt construction is one in which the cordconstruction is 840/1/2 or 840/1/3 and the cord spacing is 30 cpi.

[0022] Finally, in certain embodiments, the axial or lateral spacingbetween the polyamide 6.6 twisted cords is approximately 30 cords perinch (cpi) to approximately 26 cpi, while in one embodiment, the spacingis approximately 30 cpi.

[0023] In one embodiment, the drive belt 16 is a polyribbed belt sinceit includes a plurality of longitudinal grooves 24 cut into the innersurface of the belt, forming a complimentary plurality of ribs 26, wheresuch ribs and grooves 24, 26 are received within corresponding ribs 28and grooves 30 on the pulleys 12, 14. The number of ribs in the belt canvary. The width (number of ribs) can be selected to provide the tensionthat is desired. Belts having 2, 3, 4, 6 and up to 25 or more ribs areknown in the art. Although the figure illustrates a polyribbed belt, theinvention can also take the form of a flat belt, a V-belt or a bandedV-belt.

[0024] Before installation on the accessory drive 10, in certainembodiments, the length of the belt 16 is approximately 2% toapproximately 3% lower than the nominal drive length between the drivepulley 12 and accessory pulley 14 (where the nominal drive length is thelength of a taut belt when carried on the drive pulley and accessorypulley; or, if more than two pulleys are used in the accessory drivesystem, the nominal drive length is the length of a taut belt whencarried on all the pulleys of the accessory drive system). In theexemplary embodiment, the length of the drive belt 16, beforeinstallation on the pulleys, is approximately 2.2% to approximately 2.3%lower than the nominal drive length between the drive pulley 12 and theaccessory pulley 14. Such a reduced length of the drive belt 16, incombination with the construction of the drive belt 16 as discussedherein, provides the drive belt with an operational drive tension ofapproximately 111 N (25 lbf.) to approximately 200 N (45 lbf.) over theoperational life of the belt 16, which, for a three-ribbed belt, istypically 241,401 Km (150,000 miles) of operation for the automobile onwhich the belt 16 is used. Operational life will change for otherconfigurations of the belt, i.e., 6-rib belt configurations.

[0025] In one embodiment, the belts 16 are produced utilizing a novelversion of the fabrication method commonly known as the “flycut” method.This involves the application of cover a layer of bias cut frictionfabric (woven, non-woven, knit, etc.) or rubber material to an outersurface of a cylindrical drum; applying a layer of cushion stock rubberover the layer of friction fabric on the drum; spinning the polyamide6.6 twisted cords around the drum at a predetermined spacing andtension, applying an optional second layer of the cushion stock rubberaround the cords spun over the first layer of cushion stock rubber,applying a layer of relatively strong and wear-resistant fiber loaded,rubber material to the drum over the second layer of cushion stock (orover the wound cords if no optional second layer of cushion stock used),curing the layers wrapped on the drum (using high-pressure steam, forexample) such that the layers of cushion stock rubber material flowaround the polyamide 6.6 twisted cords and bond to the cover layer ofbias-cut friction fabric and to the layer of strong and wear-resistant,fiber loaded, rubber material. Once cured, the composite layers areremoved from the curing area or vessel (high-pressure steam) and cooledto stop the curing process. Next, the tubular sleeve of cured compositematerial is cut into the individual belts and the belts are taken to aprofiling machine so that the grooves can be cut into the outer surfaceof the belts. Once the grooves are cut the belts may be turned insideout for use on the accessory drive system.

[0026] In one embodiment the polyamide 6.6 twisted cords are wound overthe first layer of cushion stock rubber at a cord spinning tension ofapproximately 15.5 N (3.5 lbf.). Additionally, as discussed above, inthe exemplary embodiment, the winds of the cord are spaced at a distanceof approximately 0.30 mm (0.012 in).

[0027] The above process is merely an exemplary process for constructingan exemplary belt according to the present invention. It will beapparent to those of ordinary skill in the art that alternatecombinations of layers, material and steps may be used and still remainwithin the scope of at least certain aspects of the present invention.For example, both layers of cushion stock rubber may be eliminated ifthe wear-resistant fiber loaded, rubber material can be cured to flowaround the cords and bond to the cover layer. It will also be apparentto those of ordinary skill in the art that the grooves may be formedinto the belt using other methods, such as grinding or molding.

[0028] The belt's tensile modulus per width is about 400 to 1500 N/mm.In a more particular embodiment, the tensile modulus per width of thebelt is about 400 to 1200 N/mm. In a still more particular embodiment,the tensile modulus per width of the belt is about 600 to 1000 N/mm. Thebelt 16 of the present invention provide a tensile modulus of, in anumber of embodiments, at least approximately 7000 N/mm/mm (1575lbf/in/in); and in more detailed embodiments, approximately 7800 N/mm/mm(1750 lbf/in/in) to approximately 8500 N/mm/mm (1910 lbf/in/in); and inthe exemplary embodiment, approximately 8500 N/mm/mm (1910 lbf/in/in).Therefore, the belt according to the exemplary embodiment is a lowmodulus belt with a relatively high elongation throughout theinstallation range. The belt of the exemplary embodiment has been foundto maintain a relatively high percentage of its install tension(approximately 40% to approximately 60% of its install tension)throughout the life of the belt, in both cold “non-operating” conditionsand in hot “operating” conditions. Such a belt is specifically capableof being installed over the pulleys of the accessory drive by“stretching” the belt over the pulleys; and additionally, the belt isspecifically designed to maintain a desired tension throughout thedesign life of the drive. Because the belt has a relatively low tensilemodulus, the tensile force at installation is greatly reduced ascompared to conventional belts of this type. For example, the installtension useful with the belt system of the invention can be about 20%lower than with competitive stretchy belts. More particularly, thestandard bearing life calculation for ball bearings as reported in: (1)Mechanical Engineering Design—Fourth Edition, Shigley and Mitchell,McGraw-Hill Book Company, Copyright 1983, (2) NTN Ball and RollerBearings—Technical Data, NTN Corporation, 1990, page A-40, 41, and (3)Ball Screw Support Bearings Manual: Engineering/Fatigue Life/Bearings,page 106 is:

[0029] L=(C/P)3

[0030] where: L is Basic Rated Life (106 revolutions) for 90% of atypical group of apparently identical bearings; C is Basic Dynamic LoadRating, and P is Radial Load. For comparison, the basic dynamic loadrating C can be considered constant while the radial load P is 0.8 P forthe belt in this embodiment and P for a higher modulus belt. Therefore,for a given radial load P as provided by a competitive higher modulusstretchy belt, the belt in this embodiment of the invention will provide0.8 P, which will increase the Basic Rated Life of the bearings byapproximately a factor of 1.95 (i.e. almost 100% increase). This can beshown by substituting 0.8 P in the equation above. Thus, by reducing thenominal belt tension by 20%, overall bearing life (ball bearings) can beincreased by approximately a factor of 2 based on the bearing lifecalculation provided above.

[0031] Following from the above description summaries, it should beapparent to those of ordinary skill in the art that, while the apparatusand processes herein described constitute exemplary embodiments of thepresent invention, it is to be understood that the invention is notlimited to these precise apparatuses and processes and that changes maybe made therein without departing from the scope of the invention asdefined by the claims. Additionally, it is to be understood that theinvention is defined by the claims and it is not intended that anylimitations or element describing the exemplary embodiments herein areto be incorporated into the meanings of the claims unless suchlimitations or elements are specifically listed in the claims. Likewise,it is to be understood that it is not necessary to meet any or all ofthe identified advantages or objects of the present invention disclosedherein in order to fall within the scope of any claim, since theinvention is defined by the claims and since inherent and/or unforeseenadvantages of the present invention may exist even though they may notbe explicitly discussed herein.

What is claimed is:
 1. A multiple-pulley accessory drive system for anautomobile, comprising: a drive pulley; at least one accessory pulleyoperatively coupled to an accessory drive shaft, the drive pulley andaccessory pulley having a nominal drive length therebetween; and anendless drive belt engaged between the drive pulley and the accessorypulley, the drive belt including an endless band of rubber compositematerial having a plurality of circumferentially extending and axiallyaligned, polyamide 6.6 twisted cords formed therewithin and having atensile modulus per width of about 400 to 1500 N/mm.
 2. Themultiple-pulley accessory drive system 1 wherein the tensile modulus perwidth is about 400 to 1200 N/mm.
 3. The multiple-pulley accessory drivesystem 2 wherein the tensile modulus per width is about 600 to 1000N/mm.
 4. The multiple-pulley accessory drive system of claim 3, whereinthe circumferential length of the endless drive belt, beforeinstallation on the pulleys, is approximately 2% to approximately 3%lower than the nominal drive length of the accessory drive system. 5.The multiple-pulley accessory drive system of claim 4, wherein thecircumferential length of the endless drive belt, before installation onthe pulleys, is approximately 2% to approximately 2.3% lower than thenominal drive length of the accessory drive system.
 6. Themultiple-pulley accessory drive system of claim 4, wherein the axialdistance between the cords is approximately 0.8 mm to approximately 1.0mm.
 7. The multiple-pulley accessory drive system of claim 6, whereineach twisted cord includes one or more cord yarns twisted together. 8.The multiple-pulley accessory drive system of claim 7, wherein eachtwisted cord includes a pair of cord strands twisted together.
 9. Themultiple-pulley accessory drive system of claim 4, wherein the twistedcords are axially distributed at a distribution of approximately 26 toapproximately 30 of the twisted cords per inch.
 10. The multiple-pulleyaccessory drive system of claim 1, wherein the endless drive belt has atensile modulus of at least approximately 7,000 N/mm/mm (1575lbf/in/in).
 11. The multiple-pulley accessory drive system of claim 10,wherein the endless drive belt has a tensile modulus of approximately7,800 N/mm/mm (1750 lbf/in/in) to approximately 8,500 N/mm/mm (1910lbf/in/in).
 12. The multiple-pulley accessory drive system of claim 4,wherein the operational torque of the accessory drive system is lessthan, or equal to approximately 2.7 N-m (2 ft-lb).
 13. Themultiple-pulley accessory drive system of claim 12, wherein theaccessory is an automotive water pump and the accessory pulley isoperatively coupled to a drive shaft of the water pump.
 14. Themultiple-pulley accessory drive system of claim 4, wherein the accessorydrive system is a two-pulley accessory drive system.
 15. Amultiple-pulley accessory drive system for an automobile, comprising: adrive pulley; at least one accessory pulley operatively coupled to anaccessory drive shaft, the drive pulley and accessory pulley having anominal drive length therebetween; and an endless drive belt engagedbetween the drive pulley and the accessory pulley, the drive beltincluding an endless band of rubber composite material having aplurality of circumferentially extending and axially aligned cordsformed therewithin; wherein the endless drive belt has a tensile modulusof at least approximately 7000 N/mm/mm (1575 lbf/in/in).
 16. Themultiple-pulley accessory drive system of claim 15, wherein thecircumferential length of the endless drive belt, before installation onthe pulleys, is approximately 2% to approximately 3% lower than thenominal drive length of the accessory drive system.
 17. Themultiple-pulley accessory drive system of claim 16, wherein thecircumferential length of the endless drive belt, before installation onthe pulleys, is approximately 2% to approximately 2.3% lower than thenominal drive length of the accessory drive system.
 18. Themultiple-pulley accessory drive system of claim 17, wherein the cordsare polyamide twisted cords.
 19. The multiple-pulley accessory drivesystem of claim 15, wherein the operational torque of the accessorydrive system is less than, or equal to approximately 2.7 N-m (2 ft-lb).20. The multiple-pulley accessory drive system of claim 19, wherein theaccessory is an automotive water pump and the accessory pulley isoperatively coupled to a drive shaft of the water pump.
 21. Themultiple-pulley accessory drive system of claim 20, wherein theaccessory drive system is a two-pulley accessory drive system.
 22. Themultiple-pulley accessory drive system of claim 15, wherein the endlessdrive belt has a tensile modulus of approximately 7,800 N/mm/mm (1750lbf/in/in) to approximately 8,500 N/mm/mm (1910 lbf/in/in).
 23. Themultiple-pulley accessory drive system of claim 22, wherein thecircumferential length of the endless drive belt, before installation onthe pulleys, is approximately 2% to approximately 3% lower than thenominal drive length of the accessory drive system.
 24. Themultiple-pulley accessory drive system of claim 23, wherein thecircumferential length of the endless drive belt, before installation onthe pulleys, is approximately 2% to approximately 2.3% lower than thenominal drive length of the accessory drive system.
 25. Themultiple-pulley accessory drive system of claim 24, wherein the cordsare polyamide twisted cords.
 26. The multiple-pulley accessory drivesystem of claim 15 wherein the endless drive belt has a tensile modulusof approximately 8500 N/mm/mm (1910 lbf/in/in).
 27. The multi-pulleydrive system, of claim 4 wherein the drive belt is adapted to bemanually stretched on the plurality of pulley at an install tension, andthe drive belt maintains at least approximately 40% of the installtension throughout a useful life of the drive belt.
 28. The multi-pulleydrive system of claim 27, wherein the drive belt maintains at leastapproximately 40% to approximately 60% of the install tension throughoutthe useful life of the drive belt.
 29. A method for fabricating anaccessory drive belt, comprising the steps of: applying at least a layerof cover material to an outer circumferential surface of a drum;applying at least a first layer of cushion stock rubber material to thedrum over the cover layer; winding a polyamide 6.6 twisted cord to thedrum over the first layer of cushion stock; applying a layer ofrelatively strong and wear resistant, fiber loaded, rubber material tothe drum over the polyamide 6.6 twisted cord; curing multiple layerstogether into a cured sleeve of belt composite material; cutting thecured sleeve into a plurality of endless belts; and turning the endlessbelts inside-out for use as an accessory drive belt; wherein thepolyamide 6.6 twisted cord is wound in the winding step at approximately13 N (3 lbf.) to approximately 15.5 N (3.5 lbf.).